A universal electrical power plug that enables direct connection of a power cord to a power source obviously is preferable to an adaptor which mates the power cord with the source. Adaptors can get lost. Also, they are not acceptable in most countries as a mode to correct an appliance with a power source. A universal plug can desirably reduce weight in products, such as laptop computers, that are user moved between and/or sold to nations with different standards for their power source outlets. Finally, use of a universally acceptable power plug reduces the variety of different plug configurations and hence the amount of inventory required for internationally marketed products.
Numerous configurations of universal electrical power plugs or adaptors have heretofore been proposed. The following constitutes the prior art known to applicant considered most pertinent to the present invention.
PCT WO 93/11588 discloses an electrical adaptor configured to permit an electrical plug with contact pins according to one national standard to be inserted into apertures in a power outlet arranged according to another national standard. Contact pins or prongs are slidably retained in elongated holes in a pin housing. A rotatable selector plate permits contact pins appropriate to a selected national standard to be uncovered, withdrawn from the retaining holes, then manually screw threaded into threads provided adjacent to the outer ends of the holes. A cowling, which encircles the pin housing, is normally spring biased to cover the contact pins, as required by a German standard; but the cowling is forced back against the spring bias to expose the contact pins as the adaptor is mated with the wall outlet.
U.S. Pat. No. 4,626,052 discloses a multipin adaptor comprising a plurality of slidable carriers, each carrying an array of contact pins that suits a respective national standard. By manually sliding the appropriate carrier, the proper array of pins is extended and locked. The pins remain extended until a lug is depressed and flees a detent to permit manual retraction of the carrier and thereby of the pin array.
U.S. Pat. No. 4,543,624 is of interest as showing a pair of two-part contact pins, each having a flat front part and a cylindrical rear part that has limited rotation about its axis. This permits the front parts to be rotated to parallel for an American socket and angled for an Australian/New Zealand socket.
Other prior art considered to be of incidental interest but showing still other configurations of electrical power plugs or adaptors are U.S. Pat. Nos. 4,815,983, 4,518,212, and 3,025,486; and United Kingdom Patent GB 2,097,202A.
There is a need for a universal electrical power plug that (i) senses and automatically selects the appropriate configuration of contact prongs as the plug engages a wall outlet or other receptacle; (ii) requires no manual selection or screw threading; (iii) is compact, requiring no more volume than a conventional British power plug; and (iv) can adapt to standard U.S., European, British, German, and Australian/New Zealand sockets.